The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefore.
Not applicable.
(1) Field of the Invention
The present invention relates generally to sonar displays and, more particularly, to a system and method suitable for displaying the outputs of multiple broadband processors with different detection algorithms whereby each multiple broadband processor operates on N-channels of sonar data from a towed array.
(2) Description of the Prior Art
It is well known that submarines and other vessels may utilize different types of towed arrays of sonar sensors for receiving sonar data. The towed array may typically have some number, N, of channels wherein the number of channels is typically related to the number of sonar detectors in the array. For instance, there may be one channel output for each acoustic sensor input to provide for conservation of energy with respect to each sensor. Each channel output may typically be considered as a beam xe2x80x9cpointed toxe2x80x9d a particular listening direction. With fewer beam outputs, information is lost. With more beams, the outputs are merely interpolated values of the input set. So if, for example, there are N=10 sensor inputs, then there may be N=10 independent beam outputs steered in N=10 different directions.
The information is processed to determine various attributes of targets. For instance, bearing is a measure (as a function of time) of the angle to the target (or acoustic source) relative to true North or relative to the direction of the ship""s heading. Bearing rate is the rate of change of the bearing with respect to time. High bearing rate contacts are close to the array and tend to be relatively easy to spot. With respect to relative bearings, low bearing rate contacts tend to fall into one of three categories: opening away, running on parallel velocity, or on a collision course.
For processing the data received by the particular type of towed sonar array, different types of broadband detection processing schemes may be used. Each type of broadband detection processing scheme will typically have different advantages and disadvantages depending on the particular type of scenario of use. However, in the past, the output of each broadband detection processing scheme has required a separate display format. Due to the difficulty of viewing two different displays concurrently or one at a time, it would be desirable to provide a single display, such as a single bearing versus time history display, whereby the relative advantages of each type of detection scheme are built into a single display format.
Patents that show attempts to solve the above and other related problems are as follows:
U.S. Pat. No. 5,481,505, issued Jan. 2, 1996, to Donald et al., discloses a method and apparatus for detecting, processing and tracking sonar signals to provide bearing, range and depth information that locates an object in three-dimensional underwater space. An inverse beamformer utilizes signals from a towed horizontal array of hydrophones to estimate a bearing to a possible object. A matched field processor receives measured covariance matrix data based upon signals from the hydrophones and signals from a propagation model. An eight nearest neighbor peak picker provides plane wave peaks in response to output beam levels from the matched processor. A five-dimensional M of N tracker identifies peaks within the specified limit of frequency, bearing change over time, range and depth to specify an object as a target and to display its relative range and depth with respect to the array of hydrophones.
U.S. Pat. No. 5,251,185, issued Oct. 5, 1993, to P. M. Baggenstoss, discloses an improved sonar signal processor and display combining the use of both coherent and incoherent signal processors. In addition to a conventionally used matched filter detection processor, an incoherent signal processor comprising a cross-range energy filter and a down-range energy filter is used. The cross-range energy filter detects objects characterized by a narrow bearing response; whereas the down-range energy filter detects objects characterized by a narrow range response. The detection events resulting from the incoherent signal processor are displayed in a subdued color to prevent distraction from the primary display events and to reduce the false alarm rate by allowing the sonar operator to view events in the context of natural boundaries.
U.S. Pat. No. 5,216,640, issued Jun. 1, 1993, to Donald et al., discloses an apparatus and method for detecting, processing, and tracking sonar signals. Plane wave energy from the sonar signal source is measured at multiple points using an array of plane wave energy receptors. These measurements are processed using an inverse beamformer to generate output beam levels. These output beam levels are then processed using the spectrum normalizer to yield spatially and spectrally normalized output beam levels. The normalized beam levels are then processed using an eight nearest-neighbor peak-picker to provide plane wave peaks. Finally, the plane wave peaks are processed by a three-dimensioned M of N tracker to identify peaks within a specified limit of frequency and angle change over time. The identified peaks may be displaced or recorded for further analysis.
U.S. Pat. No. 5,058,081, issued Oct. 15, 1991, to Gulli et al., discloses a method of formation of channels for a sonar after being sampled at a frequency T=1/4f0 (where f0 is the receiving center frequency of the sonar) the signals from the hydrophones of the sonar and having translated them to baseband, the signals thus translated are subsampled with a period TSE=kT (wherein k is an integer) substantially equal to 1.25 B, where B is the reception bandwidth of the sonar. A first set of signals is subsampled at identical times to form a frontal sector. Two further sets of signals are subsampled with delays between the signals from two adjacent hydrophones equal to T, which determines two side sectors adjacent to the frontal sector. The subsampled signals are then transmitted serially by the towing cable of the sonar device towed array and are processed in FFT circuits which allow to form in each sector a set of channels covering the sector. This allows to considerably reduce the data transmission rate between the towed portion of the sonar and the portion located in the towing ship.
U.S. Pat. No. 4,935,748, issued Jun. 19, 1990, to Schmidt et al., discloses a blast recorder and method for monitoring and processing vibrations from blasts, and for displaying the results in a nearly real time basis and in a manner which is easily interpreted by a relatively unskilled field worker and corresponds to a form which closely correspond to the real damage causing aspect of the blast than heretofore. The invention operates by receiving seismic energy signals from a blast sensor, processing the energy signals to obtain velocity signals relating to said blast, filtering either the energy signals prior to, or the velocity signals following said processing step, into high and low frequency bands, to obtain high and low band velocity signals, integrating over the period of the blast the high and low band velocity signals to obtain high and low band displacement signals, determining the peak velocity signal in each band, over the period of the blast, and displaying one or all of the peak of the velocity signal determined in the high frequency band, the peak of the velocity signal determined in the low frequency band, and the displacement signal related to the low frequency band.
U.S. Pat. No. 3,713,087, issued Jan. 23, 1973, to Bauer et al., discloses an acoustical detection apparatus for determining the direction of origin of sounds. A first acoustic receiving system having a relatively high uniform sensitivity in a predetermined plane and a relatively low sensitivity in and about the direction perpendicular to the plane is provided. A second acoustic receiving system having a spherical sensitivity pattern is also provided. The sensitivity of the second system is set substantially equal to the sensitivity of the first system in the predetermined plane. Means are provided for comparing the outputs of the first and second systems, the ratio of these outputs indicating the direction from which received sounds are arriving. In a preferred embodiment, of the invention, the first acoustic receiving system has a donut-shaped reception characteristic.
The above cited prior art which does not show a suitable means for combining the results of multiple broadband detection processing schemes to thereby produce a single display wherein the advantages of each type of broadband detection scheme are incorporated without the need for viewing multiple displays concurrently or consecutively. Those skilled in the art will appreciate the present invention that addresses the above and other problems.
Accordingly, it is an object of the present invention to provide an improved sonar system and method.
It is another object of the present invention to provide a system with one or more processes for combining the outputs from multiple broadband detection schemes.
It is yet another object of the present invention to provide a sonar operator with a single bearing versus time history display which is based on the outputs of two passive broadband detectors.
An advantage of a system in accord with the present invention is that it is less likely to miss an acoustic contact.
A feature of the present invention, in one embodiment, is the use of at least two detectors operating on data supplied through each sonar data channel to effectively split the data path whereby the data is processed in several ways simultaneously and subsequently recombined into one data path.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. It will be understood that above listed objects and advantages of the invention are intended only as an aid in understanding aspects of the invention, are not intended to limit the invention in any way, and do not form a comprehensive list of objects, features, and advantages.
In accordance with the present invention, a system for displaying sonar data is provided which can comprise elements such as a sonar array with a plurality of sonar sensors and a plurality of data channels. The plurality of data channels can be split to form a plurality of first detector channels and a plurality of second detector channels. A plurality of comparators may be utilized for selecting an output from each of the first detector channels and each of the second detectors. A display can be provided for displaying a comparator output for each of the plurality of comparators. The plurality of comparators can in one embodiment each utilize a binary OR operation selecting from the first detector channel and the second detector channels. The OR operation can be of the type which selects a maximum value from each of the first detector channels as compared with each of the second detector channels when the outputs of the detector channels are not strictly binary.
The system can further comprise a plurality of first normalizers for the plurality of first detector channels, and a plurality of second normalizers for the plurality of second detector channels. The comparators can be used select a maximum output from the first normalizers as compared to the second normalizers. Preferably, the first detector channels and the second detector channels utilize different types of broadband detection schemes. In a preferred embodiment, each of the first detector channels utilizes a Smooth Coherence Transform (SCOT) processor and each of the second detector channels utilize a Sub-band Peak Energy Detection (SPED) processor. In one embodiment, the display is a bearing versus time history display.
A method is also provided for displaying the sonar data which may comprise one or more of the following steps such as processing sonar data through a plurality of data channels, splitting each of the plurality of data channels for processing by at least two different detection processors, recombining each of the split data channels to form a plurality of recombined data channels, and utilizing data from each of the plurality of recombined data channels for a display. The processing may comprise simultaneously utilizing a first detector and a second detector. The step of recombining may further comprise executing a binary OR operation on an output related to the first detector and the second detector to produce a plurality of OR outputs. Other steps may include displaying the plurality of OR outputs on the display and/or scaling the outputs of the first detector and the second detector prior to the step of executing the OR operation.
In one particular embodiment of the invention, a SCOT OR SPED (SOS) method is provided for displaying sonar data which may comprise one or more steps such as providing N channels of sonar data, detecting each of the N channels of sonar data with a plurality of SPED detectors, detecting each of the N channels of sonar data with a plurality of SCOT detectors, and producing channels of data for display by performing a binary OR operation between a SPED output for each respective SPED detector and a SCOT output for each respective SCOT detector for each of the N channels of sonar data. Other steps may include scaling and aligning each SPED detector output and each SCOT detector output prior to the step of performing the OR operation. The OR operation may comprise selecting a maximum of the SPED output as compared to the SCOT output. Other steps may include displaying the N channels of data for display in a bearing versus time history display format. Additional or alternative steps may include producing the N-channels of sonar data with a beamformer and applying data from a towed array with a plurality of sonar sensors to the beamformer.